Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $248.28   8.219%   $268.6861   $268.69   $268.70   $268.70  
  Purchase #2 $85.81   12.127%   $96.2162   $96.22   $96.20   $96.20  
  Purchase #3 $6.37   4.750%   $6.6726   $6.67   $6.65   $6.70  
  Purchase #4 $172.72   7.595%   $185.8381   $185.84   $185.85   $185.80  
  Purchase #5 $199.53   3.279%   $206.0726   $206.07   $206.05   $206.10  
  Purchase #6 $208.27   5.342%   $219.3958   $219.40   $219.40   $219.40  
  Purchase #7 $245.66   9.625%   $269.3048   $269.30   $269.30   $269.30  
  7 purchase totals = $1,166.64       $1,252.1862   $1,252.19   $1,252.15   $1,252.20